Diffusion coating of metals



June 21, 1966 R. P. SEELIG 3,257,227

DIFFUSION COATING OF METALS Filed Dec. 31, 1962 2 Sheets-Sheet 1 "in? I 32 33 INVENTOR.

F/[lwp P SEEL/ June 21, 1966 R. P. SEELIG 3,257,227

DIFFUSION CQATING OF METALS Filed Dec. 31, 1962 2 Sheets-Sheet 2 FIG. 2

United States Patent 3,257,227 DIFFUSION COATING 0F METALS Richard P. Seelig, Elmsford, N.Y., assignor to Chromalloy American Corporation, a corporation of New York Filed Dec. 31, 1962, Ser. No. 248,599

12 Claims. (Cl. 117--66) This invention relates to the coating or treating of metal articles by diffusing into the surface thereof a different metal or combination of metals to provide a surface layer or case thereover and, more particularly, to such diffusion coating techniques utilizing a powdered composition or mixture as the source of the treating materials and wherein the metal to be coated or treated is in the form of long sheets or strips rolled into convolute rolls.

As is now well understood in the art of diffusion coating, techniques generally of the character to which this invention relates may include embedding metal articles to be coated in a dry powdered pack including a source of the coating metal, a highly reactive energizer material for effecting transfer of the coating metal to the surface of the article to be coated in diffusible form and a refractory filler material, in which pack the articles are heated to accomplish the diffusion coating at high temperature in a reducing or other controlled non-oxidizing atmosphere in a sealed or closed retort. Alternatively, and particularly where the size or shape of the metal article to be coated is not readily susceptible of embedding in a pack of coating composition, the composition in powdered or slurry form is otherwise applied or maintained in-contact with the surface of the metal articles during the heating and diffusing steps-as, for example, disclosed in the co-pending application of Robert Samuel, Ser( No. 801,994, filed March 26, 1959, now US. Patent No. 3,061,492, regarding diffusion coating of stacks of large sheets or bundles of rods, and the like.

A wide variety of sheet metal materials, however, are manufactured in the first instance as long strips of sheet metal (e.g., rolled sheet steel), which strips are formed at the point of manufacture into convolute rolls or coils for ease in handling and transportation to the point of use. Indeed, a variety of fabricating and manufacturing .operations in'which various metal articles are made from such coiled sheet metal strips or sheets are particularly arranged to receive the sheet metal raw material in the form of rolls or coils automatically handled by the fabricating machinery. In some such instances, it is desirable to have such sheet metal duifusion coated for one purpose or another prior to use or fabrication or while still in convolute rolled form, and techniques for accommodating such a situation are disclosed, for example, in the co-pending application of Commanday and Martin, S.N. 781,824, filed October 27, 1958, now U.S. Patent No. 3,163,553. With such techniques, as will be understood, the long strip or web of sheet metal may be rolled into convolute form with the simultaneous introduction of a layer of powdered coating composition between the successive convolutions, and the finished coil, including the coating compositions distributed between adjacent convolutions thereof, may be introduced into a scalable retort for the heating and diffusing steps whereby diffuice considered as utilizing an unnecessary large amount of space in whatever heating apparatus is used, while also increasing the cost of processing and operation by virtue of, for example, wasting whatever amount of heat is required to heat the mass of the retort itself and/or prolonging and delaying both the time to heat up to treating temperature and the length of the cooling cycle following treatment. Similarly, whereas conventional apparatus is readily available for handling such large rolls of sheet metal individually or in groups, and even while quite hot, the necessity for enclosing such rolls in a sealed retort during the coating step also interjects a further complication or expense or diificulty in the handling and processing of the rolls, especially on a large scale commercial basis where simplicity of processing and automatic handling of the individual rolls may be a matter of substantial significance for profitable operation.

According to this invention, however, there are provided techniques and apparatus arrangements for retorts or other sealed or treating containers for the coils during the heating and diffusion coating steps, but with the finished coils themselves in accordance herewith being formed as self-enclosing retorts. As illustrative of satisfactory embodiments of this invention may be noted the provision of an end plate or cover welded or otherwise affixed to one or both ends of the coil and unified with the outer convolution to provide a sealed casing enclosing the outer convolutions of the roll and the coating composition interspersed therebetween for the treating steps as may be carried simply by placing the self-enclosed and sealed coil in whatever furnace or heating apparatus is desired, and, preferably, with means in such end cover or outer convolution casing for withdrawing or introducing or controlling gaseous material to maintain the desired orrequired atmosphere within the casing and coating composition therein for the diffusion coating reaction.

It is to be understood that this invention and the teachings thereof include and are' adapted to the diffusion coating of a wide variety of ferrous and non-ferrous sheet metal materials with a similarly wide variety of refractory or oxidation-resistant or other coating metals or substances susceptible, as well recognized, to satisfactory diffusion from a treating pack or composition into the surface of a metal article, although, primarily for simplicity, this invention will be 'illustratively explained primarily with regard to the diffusion coating of materials such as chromium into the surfaces of sheets or webs of iron or steelmaterials.

With all the foregoing and additional objects in view, this invention will now be explained in more detail, and objects and advantages thereof will be apparent from the following description, the accompanying drawings, and the appended claims.

In the drawings:

FIG. 1 is a side elevation of coil winding and coating compound feeding mechanism and apparatus in accordance herewith;

FIG. 2 is an end elevation view of the apparatus of FIG. 1 from the left hand end thereof;

FIG. 3 is a fragmentary and somewhat diagrammatic view on a larger scale indicating feeding mechanism for introduction of the coating compound into the convolutions of the metal strip being coiled;

' FIG. 4 is a partial transverse detail of the braking device of the illustrative mechanism and taken on the line 4-4 of FIG. 3;

- FIG. 5 is a fragmentary enlarged detailed view of the coil of sheet metalstrip being wound, illustrative of the delivery of coating compound thereto and the accommodation of the compound between the roll convolution;

FIG. 6 is a perspective showing of the wound coil with sealed outer convolution and end closing plates fixed thereto as embodying and for practicing this invention; and

FIG. 7 is a vertical section, partly broken away, of a sealed coil embodying and for practicing this invention disposed in one manner in accordance herewith for introduction to a furnace for the heating and diffusion coating steps.

Referring 'to the drawings, in which like reference characters refer to like parts throughout the several views thereof, there is illustrated mechanism with which satisfactory results have been acieved in accordance herewith for winding a web of sheet metal into a convolute roll and for feeding coating compound between successive convolutions thereof, although it is to be understood that a variety of different apparatus or mechanisms are satisfactorily available for accomplishing such results in accordance herewith. Thus, FIGS. 1 and 2 illustrate such apparatus as comprising a main frame structure including a base 10, uprights 11 and 12 supporting horizontal members 13 all in such manner that a coil 14 of sheet metal to be diffusion coated or treated in accordance herewith is supported for rotation on rollers 15 and has its horizontal displacement limited between rolls 16 and 17. Frame member 12, together with horizontal members 17, support a supply hopper 18 from which the powdered or comminuted coating compound composition (indicated by 19) is delivered to the feeding mechanism, generally indicated at 20. The strip of sheet metal, indicated at 21, is withdrawn or unwound from coil 14 as the roll rotatably rests on and between rollers 15-17, as will be understood, and web 21 passes through a braking device 22 and thence over roll 23, carried by shaft 24, to be wound on an expanding type (radially collapsible) mandrel or roll core 25 projecting centrally from a face plate or disc 126 having a shaft 26 journaled in bearings 27 and mounted on oscillating arms 28 which may be swung on shaft 29.

Suitable provision is made to serve the dual functions of urging the rolls 23 and 25 together at substantially uniform pressure, and to permit such progressive displacement of roll 25 as will accommodate the increasing diameter of the coil of strip 21 being wound thereon. Satisfactorily such means comprise an arm 60 projecting laterally from one of the arms 28 and constantly urged upwardly by piston 61 having its piston rod pivotally connected at 62 to arm 60, the cylinder 63 having a pivotal mounting at 64 and being supplied with pressure fluid at substantially constant pressure through line 65. The constantly applied force exerted by piston 61 swings arms 28 and roll 25 toward roll 23 to maintain a substan tially constant pressure between the two rolls at the line of contact thereof below the nip or throat 47 therebetween, the piston 61 however being displaceable downwardly within the cylinder 63 to permit movement of roll 25 away from roll 23 in accordance with the progressive increase in the diameter of the convolute roll of strip 21 being formed.

The brake arrangement 22 is shown as comprising a pair of pressure pads 32 bearing against opposite sides of web '21 passing therebetween, and, confined between support 33 and member '34 movable with a pressure screw arrangement 35 extending through a stationary supported threaded sleeve 36 and rotatable by handle 37 to vary the braking confinement or force applied to the sheet metal web 21 and therefore its resistance to advancement. Brake 22 is so adjusted as to tension strip or web 21 in resistance to the winding pull of roll 25 sufiiciently to assure tracking and progressive compaction of the roll convolutions being formed on roll 25 against the treating compound being introduced between.

Winding mandrel or roll 25 is driven by motor 38 through gear box 39, chain 40 applied to sprocket 41 on shaft 29, and chain 42 passing over sprockets 43 and 44 respectively on shaft 29 and 26 Asit advances to roll 25, sheet metal strip or web 21 passes over roll 23 on shaft 24, and through the nip formed between roll 23 and the wound convolutions 30 of web 21 being formed on roll 25, thus providing a throat or trough 47 into which coating compound 19 is delivered from feeder 20. The latter is shown as comprising satisfactorily a roller 48 extending within the feeder housing 49 and carrying a sprocket 50 outside the housing for driving engagement with chain 51 from sprocket 52 on shaft 24; roll 23 and sprocket 52 being driven by frictional drive contact imparted from web 21 passing over roll 23, thus generally correlating the driving speed of roll 48 with the lengths of web 21 passing over roll 23. Powdered or comminuted compound or composition19 passes through slot 53 in the bottom of hopper 18, on to roll 48 for metering control of the feed rate as governed by the rotating speed of roll 48, which is in turn governed to assure delivery of the coating composition into trough or throat 47 in a quantity and rate desired or satisfactory for adequate filling in between the successive convolutions 30 being formed as strip 21 is wound onto roll 25.

Coating composition 19 is introduced into the throat 47 and distributed across substantially the width of strip 21 in quantities sufilcient for treating of both metal surfaces of roll 21 forming adjacent convolutions 30 between which the coating composition is interspersed or incorporated in the coil being wound on roll 25. Thus, the quantity of coating composition, and the thickness of layers 55 thereof between adjacent convolutions 30 of web 21 is varied and controlled in accordance with such considerations as the particular composition of sheet metal 21, etc.all in known and well understood manner as may be required or desired to produce ultimately the desired finished diffusion coating result. Merely as illustrative, in the chromizing of low carbon steel strip 21, the coating composition layers 55 between adjacent convolutions 30 and the finished coil pack satisfactorily are of a thickness within the range of 0.005 to 0.20 inch. Upon the complete winding of web 21 from coil 14 into the convolute form of coil on mandrel 25, with layers 55 of coating composition uniformly distributed between adjacent convolutions 31) of the finished coil and in direct contact with substantially the entire surfaces of both sides of strip 21 throughout the coil, the finished coil is removed from mandrel 25 (in known manner, as by collapsing and withdrawing the mandrel), and the finished coil may be temporarily banded or otherwise fastened in tightly rolled form prior to the operation discussed below.

As noted above, the foregoing description and apparatus is merely illustrative of one satisfactory arrangement for providing proper winding of sheet metal strip 21 into a convolute coil and proper introduction and uniform distribution of the comminuted or powdered coating composition between adjacent convolutions thereof to achieve adequate or desired difiusion coating upon the heating and treating of the finished or coil under suitable prolonged heating steps with appropriate control and maintenance of the required non-oxidizing atmosphere; and further details of the winding and distribution of coating compositions are disclosed in the above mentioned co-pending application S. N. 781,824, now U. S. Patent No. 3,163,553, to which reference is made here to the extent which may be necessary or desired as supplementing the foregoing.

Illustrative of various coating pack compositions with which satisfactory results have been achieved herewith may be noted a variety of different dry powdered mixtures including a powdered refractory filler component, a source of the coating metal in either elemental or combined form, an energizer such as a volatilizable halide or source of halogen in either elemental or combined form, as understood in the art of dry pack diffusion coating.

More specifically, several particular satisfactory formulations may be noted:

Not only is the handling of the individual rolls complicated by a necessity for enclosing them in a separate retort, but the mass of metal in the large retort itself, of course, must be heated in the heating step along with the coiled or rolled sheet metal webs to be coated. As will be understood, the heat or power necessary to heat the retort itself, as distinct from that required to heat the metal to be treated, is essentially wasted and, the additional time for heating and cooling the retort may disadvantageously prolong or slow down the whole treating operation and/ or interject into commercial production an extra item of cost.

In accordance herewith, the need for a retort to accommodate the finished coil 70 is dispensed with and the outer convolution of the coil is converted into a sealed or enclosed casing within which the diffusion coating steps are effected. As illustrative of one satisfactory arrangement in accordance herewith, there is indicated in FIG. 6 a coiled sheet metal strip as produced by the above descri bed apparatus and as including various convolutions 30 with coating composition uniformly distributed and interspersed between. The outermost end of the sheet metal strip at the outside of the coil is welded to the outer most convolution of the strip itself, welded at 75, and

two end cover plates enclosing each end of the coil and welded to the outermost convolution all around the circumrference thereof.

A pipe connection 77 may be included in and through one of the end cover plates 76 to provide a passage for escape of air as the enclosed roll is heated, to be interrupted by valving to prevent escape of the desired non- Example '1: Parts by wt. Tabular alumina (325 mesh) 80.00 Chromium metal powder (60 mesh) 19.75 Ammonium bifluoride 0.25

Example 2:

Magnesium oxide (325 mesh) 73.00 Chromium metal powder (60 mesh) 24.75 Ammonium bifluoride 0.25

Example 3:

Refractory clay (325 mesh) a 75.00 Ferro chrome (60 mesh) 19.75 Ammoniumchloride 0.25

Example 4:

Magnesium oxide 60.0 Chromium metal powder 20.0 Chromium chloride 10.0 Magnesium met-a1 powder 10.0

Example 5:

Alumina 65.0 Chromium metal powder 20.0 Chromium fluoride 10.0 Aluminum metal powder 5.0

Example 6:

Magnesium oxide 60.0 Chromium metal powder 30.0 Chromium chloride 5.0 Calcium metal 5.0

Example 7:

Magnesium oxide 60.0 Chromium metal powder 30.0 Chromium fluoride 5.0 Silicon powder 5.0

Example 8:

Magnesium oxide 40.0 Chromium metal powder 30.0 Chromium fluoride 5.0 Nickel metal powder 15.0 Nickel fluoride 5.0 Silicon powder 5.0

As will be understood, of course, a variety of other coating materials, either diffusible metals or other elements such as silicon 'boron are satisfactorily available for the coating composition, and, as noted, the invention is applicable to a variety of different sheet metal materials or strips wound into confluent form. 'Ibus satisfactory results are achieved using, as the refractory filler component of the coating composition, such materials as alumina, kaolin, magnesia, and other inert refractory oxides. Similarly, the treating metal may be any one of a wide variety of diffusible metals or alloys such as chromium, molybdenum, tungsten, titanium, zirconium, iron, nickel, tantalum, cobalt, copper, beryllium, zinc, vanadium, etc., including mixtures thereof, depending upon the particular metal of web 21 and the particular effects desired. Typical *halogen energizer materials may also illustrative'ly be noted as various ammonium or alkali metal halides, elemental halogens, gaseous halides, etc. and mixtures thereof all in known manner.

In any event, the finished and wound coil or convolute pack thus formed, including the coating compositions, is to be enclosed in one way or another to maintain the desired non-oxidizing atmosphere and heated to effect diffusion coating. Generally, the treatment temperature is maintained within the range of about '1-200" to '2200" F. over periods of from about 4 to 6 hours or longer. As noted, the provision of a sealed or sealable metal retort for accommodating the coils of sheet metal in known or conventional manner may interject a number of complexities or disadvantages, particularly in commercial production.

oxidizing atmosphere during heating, or to provide a gas inlet for introduction of a suitably controlled atmosphere to the sealed casing around the roll during the diffusing coating step, although such connection may not be necessary in every instance. As will be apparent from the foregoing, each individual coil, welded and encased as described and as illustrated in FIG. 6, may readily be handled and individually introduced into whatever furnace or other heating apparatus is provided, and the atmosphere within the case is readily controlled as by fixing valved conduit to pipe connection 77. Thus the desired sealed enclosure for the coating step is assured, yet without the use of separate retorts and Without the difficulties incident to heating, handling, and storage thereof.

As indicated more particularly in FIG. 7, another arrangement embodying and for practicing this invention is illustrated wherein an end cover plate 76 is welded over only one end of a coil 70, while the other (bottom) end remains uncovered. As will be understood, the outer end of the strip comprising coil 70 is welded to the outermost convolution 30, as with the arrangement in FIG. 6. In this embodiment, a tray 80 is provided to hold roll 70 in the upright position shown in the furnace or other apparatus, and a fusible sealing composition 81 (such as fusible silicate cement) is introduced into a tray 80 and within and around coil 70. In this manner, as the heating step is commenced, air entrapped within the convolutions 30 expands and may escape from beneath the open bottom end of coil 70, and, hence, the pipe connection 77 (although illustrated) may not be needed. As the heating comes to temperature, however, fusible sealing comto prevent air from being drawn thereinto during cooling as the expanded hot gases within the enclosed coil pack are cooled.

Also, as indicated in FIG. 7, a suitable conduit and valve 82 is readily connected to pipe coupling 77 to control the withdrawing or preservation of the atmosphere within the sealed coil casing, and/ or to admit a reducing or inert or other gas during the coating or cooling steps as may be desired. As is indicated in FIG. 7, when end cover plate 76 is welded to the outermost convolution 30 of coil 70 (with the welded seam being indicated by $4) a slight gap or space '85 is preferably left between the intersurface of cover plate 76 and the ends of the various convolutions 30 in the coiled sheet metal strip for circulation of reactant gases, etc., during the coating step.

Upon completion of the heating and cooling cycles as required to effect the desired diffusion coating (and maintained under Whatever gas pressure or atmosphere conditions may be desired within the sealed casing), the individual coils are readily handled and removed from the heating operation or furnace, the various end cover plates 76 cut therefrom, the welded outer convolution 30 cut and discarded, and the finished and coated rolled sheet metal strip is then in a form for further shipment, handling or fabrication with all surfaces of the entire strip appropriately diffusion coated as desired. If the particular furnace or heating apparatus used herewith includes a highly oxidizing atmosphere sufficient to penetrate or oxidize through the outer convolution 30 of coil 70 during the heating cycle, the outer surface of the outermost convolution 30 and of the end closure plate 76 are sprayed or otherwise treated with heat resistant or oxidation resistant paint materials or coatings in known manner. Although, in many cases, the thickness or gauge of the sheet metal strip itself will be sufficient for the outermost convolution 30 thereof to withstand any oxidizing effects from the furnace atmosphere during the treating step. Alternatively, the furnace atmosphere can be controlled in known manner to be essentially inert or nonoxidizing if desired. The handling of either the completely self-enclosed coils of FIG. 6, or the arrangement of FIG. 7 with the coils standing on shallow trays 80, is readily accomplished in known manner and even in high production operations, by known automatic conveying and other equipment before, during and after the heating step in a furnace, and all :without either the extra space or extra heating requirement incident to enclosing the coils in sealed retorts therefor for introduction into the heating and cooling steps.

While the techniques and arrangements of apparatus disclosed herein form preferred embodiments of this invention, this invention is not limited to these particular techniques and arrangement of apparatus -and changes and modifications may be made therein without departing from the scope of this invention which is defined in the appended claims.

What is claimed is:

.1. In a method for the diffusion coating of a coating material into the surfaces of elongated strips or sheets of sheet metal, the steps which comprise winding said sheet metal into a convolute coil, uniformly distributing a comminuted treating pack composition including said coating material between adjacent convolutions of said coil during said winding of said sheet metal, sealing the outermost convolution of said coil therearound, affixing over at least one end of said coil a cover plate in sealed relation with said outermost convolution, and heating said thus-sealed coil effecting diffusion of said coating material from said comminuted composition into the surfaces of said sheet metal.

2. In a method for the diffusion coating of a coating material into the surfaces of elongated strips or sheets of sheet metal, the steps which comprise winding said sheet metal into a convolute coil, uniformly distributing a comminuted treating pack composition including said 8 coating material between adjacent convolutions of said coil during said Winding of said sheet metal, seal-ing the outermost convolution of said coil therearound, affixing over at least one end of said coil .a cover plate in sealed relation with said outermost convolution, providing in said cover plate a gas connection conduit for introducing and withdrawing gas through said cover plate, and heating said thus-sealed coil effecting diffusion of said coating material from said comminuted composition into the surfaces of said sheet metal.

3. In a method for the diffusion coating of a coating material into the surfaces of an elongated strip of sheet metal, the steps which comprise winding said sheet metal into a convolute coil, uniformly distributing a comminuted treating pack composition including said coating material and a halogen energizer between adjacent convolutions of said coil during said winding thereof, sealing the outermost convolution of said coil therearound, affixing over at least one end of said coil a cover plate in sealed relation with said outermost convolution forming therewith an enclosed treating casing for said coil, and heating said thus-sealed coil effecting diffusion of said coating material from said comminuted composition into the surfaces of said sheet metal.

4. In a method for the diffusion coating of a coating material into the surfaces of elongated sheet metal, the steps which comprise winding said sheet metal into a convolute coil, uniformly distributing a comminuted treating pack composition including said coating material between adjacent convolutions of said coil during said winding thereof, sealing the outermost convolution of said coil therearound, affixing over the ends of said coil cover plates in sealed relation with said outermost convolution forming therewith a gas-tight casing, and heating said thus-sealed coil effecting diffusion of said coating material from said comminuted composition into the surfaces of said sheet metal.

5. In a method for the diffusion coating of a coating material into the surfaces of elongated sheet metal, the steps which comprise winding said sheet metal into a convolute coil, uniformly distributing a comminuted treating pack composition including said coating material between adjacent convolutions of said coil during said winding thereof, sealing the outermost convolution of said coil therearound, affixing over one end of said coil a cover plate in sealed relation with said outermost convolution forming therewith an enclosed and gas-tight casing for said coil when said coil rest upon the end thereof opposite to said cover plate, positioning said coil on said opposite'end in a furnace, and heating said thus-sealed coil effecting diffusion of said coating material from said comminuted mixture into the surfaces of said sheet metal.

6. The method as recited in claim 5 in which a fusible sealing material is disposed around said opposite end of said coil in said furnace for gas-tight sealing around said end during said heating and diffusion step.

7. The process of diffusing into the surface of sheet metal a treating material from a source contained in a comminuted treating mixture, that includes winding the sheet metal in a convoluted roll, feeding and distributing said mixture between the roll convolutions as they are being wound to thus form a roll pack, forming from the outermost convolution of said roll a sealed casing therearound, affixing a cover plate over at least one end of said roll pack forming with said outermost convolution an enclosed treating casing, and heating the roll pack to diffuse the treating metal into the sheet metal as contained within said casing.

8. A self-contained sealed diffusion coating pack arrangement for diffusion of a coating material into the surfaces of elongated sheet metal sheets and strips upon heating of said pack arrangement, which comprises in combination a convolute coil of said sheet metal, a comminuted coating composition uniformly distributed throughout said coil and between adjacent convolutions thereof and including a source of said coating material, means for sealing the outermost convolution of said coil forming a substantially continuous circumferential casing, and cover means over at least one end of said coil and affixed in sealing engagement to said outermost convolution thereof forming therewith a gas-tight outer casing including said coil and said comminuted coating composition there- 9. A self-contained sealed diffusion coating pack arrangement for diffusion of a coating material into the surfaces of elongated sheet metal strips and sheets upon heating of said pack arrangement, which comprises in combination a convolute coil of said sheet metal, a comminuted coating composition uniformly distributed throughout said coil and between adjacent convolutions thereof and including a source of said coating material, means for sealing the outermost convolution of said coil forming a substantially continuous circumferential casing, cover means over at least one end of said coil and affixed in sealing engagement to said outermost convolution thereof forming therewith a gas-tight outer casing including said coil and said comminuted coating composition therein, and gas inlet and outlet means through said end cover means for controllably introducing and withdrawing a gas' atmosphere through said end cover means during said heating of said arrangement.

10. A self-contained sealed diffusion coating pack arrangement for diffusion of a coating material into the surfaces of elongated sheet metal upon heating of said pack arrangement, which comprises in combination a convolute coil of said sheet metal, a comminuted coating composition uniformly distributed throughout said coil and between adjacent convolutions thereof and including a source of said coating material and a source of halogen energizer therefor admixed with refractory filler, means for sealing the outermost convolution of said coil forming a substantially continuous circumferential casing, and

cover means over at least one end of said coil and aflixed in sealing engagement to said outermost convolution thereof forming therewith a gas-tight outer casing including said coil and said comminuted coating composition therein.

11. A self-contained sealed diffusion coating pack arrangement for diffusion of a coating material into the surfaces of sheet metal upon heating of said pack arrangement, which comprises in combination a convolute coil of said sheet metal, a comminuted coating composition uniformly distributed throughout said coil and between adjacent convolutions thereof and including a source of said coating material, means for sealing the outermost convolution of said coil forming a substantially continuous circumferential casing, and cover means over the ends of said coil and affixed in sealing engagement to said outermost convolution thereof forming therewith a gas-tight outer casing including said coil and said comminuted coating composition therein.

12. A meet metal pack adapted to be furnace heated for the diffusion of a treating metal into the surface of the pack metal, comprising a convolute wound roll of sheet metal, comminuted solid material contained in distributed condition between successive convolutions of the roll and comprising in addition to the treating metal source a refractory material and a halogen energizer source, means for sealing the outermost convolution of the roll to form a continuous circumferential casing therearound, and covering means over at least one end of the roll and affixed in sealing engagement with the outermost convolution forming a self-contained gas-tight casing within which the diffusion may occur upon heating of the sheet metal pack.

No references cited.

RICHARD D. NEVIUS, Primary Examiner.

A. GOLIAN, Assistant Examiner. 

1. IN A METHOD FOR THE DIFFUSION COATING OF A COATING MATERIAL INTO THE SURFACES OF ELONGATED STRIPS OR SHEETS OF SHEET METAL, THE STEPS WHICH COMPRISE WINDING SAID SHEET METAL INTO A CONVOLUTE COIL, UNIFORMLY DISTRIBUTING A COMMINUTED TREATING PACK COMPOSITION INCLUDING SAID COATING MATERIAL BETWEEN ADJACENT CONVOLUTIONS OF SAID COIL DURING SAID WINDING OF SAID SHEET METAL, SEALING THE OUTERMOST CONVOLUTION OF SAID COIL THEREAROUND, AFFIXING OVER AT LEAST ONE END OF SAID COIL A COVER PLATE IN SEALED RELATION WITH SAID OUTERMOST CONVOLUTION, AND HEATING SAID THUS-SEALED COIL EFFECTING DIFFUSION OF SAID COATING MATERIAL FROM SAID COMMINUTED COMPOSITION INTO THE SURFACES OF SAID SHEET METAL.
 8. A SELF-CONTAINED SEALED DIFFUSION COATING PACK ARRANGEMENT FOR DIFFUSION OF A COATING MATERIAL INTO THE SURFACES OF ELONGATED SHEET METAL SHEETS AND STRIPS UPON HEATING OF SAID PACK ARRANGEMENT, WHICH COMPRISES IN COMBINATION A CONVOLUTE COIL OF SAID SHEET METAL, A COMMINUTED COATING COMPOSITION UNIFORMLY DISTRUBUTED THROUGHOUT SAID COIL AND BETWEEN ADJACENT CONVOLTUIONS THEREOF AND INCLUDING A SOURCE OF SAID COATING MATERIAL, MEANS FOR SEALING THE OUTERMOST CONVOLUTION OF SAID COIL FORMING A SUBSTANTIALLY CONTINUOUS CIRCUMFERENTIAL CASING, AND COVER MEANS OVER AT LEAST ONE END OF SAID COIL AND AFFIXED IN SEALING ENGAGEMENT TO SAID OUTERMOST CONVOLUTION THEREOF FORMING THEREWITH A GAS-TIGHT OUTER CASING INCLUDING SAID COIL AND SAID COMMINUTED COATING COMPOSITION THEREIN. 